var isPC = !!window.navigator.userAgent.match(/(Windows);?[\s\/]+([\d.]+)?/);
var dpr, rem, scale;
var docEl = document.documentElement;
var fontEl = document.createElement('style');
var metaEl = document.querySelector('meta[name="viewport"]');
var win = window;

dpr = win.devicePixelRatio || 1;
scale = 1 / dpr;
rem = docEl.clientWidth * dpr / 10;

if (!isPC) {
  // 设置viewport，进行缩放，达到高清效果
  metaEl.setAttribute('content', 'width=' + dpr * docEl.clientWidth + ',initial-scale=' + scale + ',maximum-scale=' + scale + ', minimum-scale=' + scale + ',user-scalable=no');

  // 设置data-dpr属性，留作的css hack之用
  docEl.setAttribute('data-dpr', dpr);

  // 动态写入样式
  docEl.firstElementChild.appendChild(fontEl); 
  fontEl.innerHTML = 'html, body{font-size:' + rem + 'px;}'; 
}


// 给js调用的，某一dpr下rem和px之间的转换函数
window.rem2px = function(v) {
    v = parseFloat(v);
    return v * rem;
};
window.px2rem = function(v) {
    v = parseFloat(v);
    return v / rem;
};

window.dpr = dpr;
window.rem = rem;
